start_kernel函数部分分析

  //找到栈顶位置并设置个魔术字,防止堆栈 将 thread_info 的数据覆盖;
  //如果是向上生长的栈,直接通过(task_thread_info + 8K - 1)找到栈底并设置魔术字
  //内核栈大小一般为4K或者8K.
  set_task_stack_end_magic(&init_task);
    stackend = end_of_stack(tsk);
      return (unsigned long *)(task_thread_info(p) + 1);
    *stackend = STACK_END_MAGIC; // 0x57AC6E9D

//宏定义了就是向上生长
static inline unsigned long *end_of_stack(struct task_struct *p)
{
#ifdef CONFIG_STACK_GROWSUP
  return (unsigned long *)((unsigned long)task_thread_info(p) + THREAD_SIZE) - 1;
#else
  return (unsigned long *)(task_thread_info(p) + 1);
#endif
}

  int i;
  u32 mpidr = is_smp() ? read_cpuid_mpidr() & MPIDR_HWID_BITMASK : 0;
  u32 cpu = MPIDR_AFFINITY_LEVEL(mpidr, 0);

  cpu_logical_map(0) = cpu;
  for (i = 1; i < nr_cpu_ids; ++i)
    cpu_logical_map(i) = i == cpu ? 0 : i;

  /*
   * clear __my_cpu_offset on boot CPU to avoid hang caused by
   * using percpu variable early, for example, lockdep will
   * access percpu variable inside lock_release
   */
  set_my_cpu_offset(0);

  pr_info("Booting Linux on physical CPU 0x%x\n", mpidr);

static inline bool is_smp(void)
{
#ifndef CONFIG_SMP
  return false;
#elif defined(CONFIG_SMP_ON_UP)
  extern unsigned int smp_on_up;
  return !!smp_on_up;
#else
  return true;
#endif
}

  // 禁止本地中断
  local_irq_disable
    raw_local_irq_disable
      arch_local_irq_disable

  // 设置boot cpu
  boot_cpu_init
    smp_processor_id
      raw_smp_processor_id
        current_thread_info()->cpu
    set_cpu_online
    set_cpu_active
    set_cpu_present
    set_cpu_possible

  page_address_init
    // page_address_htable 是个全局结构体数组, 
    for (i = 0; i < ARRAY_SIZE(page_address_htable); i++)
      INIT_LIST_HEAD(&page_address_htable[i].lh);
      spin_lock_init(&page_address_htable[i].lock);

/* FIXED STRINGS! Don't touc.h! */
const char linux_banner[] =
  "Linux version " UTS_RELEASE " (" LINUX_COMPILE_BY "@"
  LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION "\n";

#define UTS_MACHINE "arm"
#define UTS_VERSION "#9 SMP PREEMPT Sat Dec 25 20:49:44 CST 2021"
#define LINUX_COMPILE_BY "zrc"
#define LINUX_COMPILE_HOST "zrc"
#define LINUX_COMPILER "gcc version 4.9.4 (Linaro GCC 4.9-2017.01) "

  // 初始化体系相关的部分,实现与体系和芯片有关
  setup_arch(&command_line)
    setup_processor(); // 从硬件获得体系相关的信息，并将该信息用于系统的初始化
    // __atags_pointer 指向 DTB 所在的物理地址
    mdesc = setup_machine_fdt(__atags_pointer)